Signal generator

Discussion in 'The Projects Forum' started by simo_x, Jun 11, 2011.

  1. simo_x

    Thread Starter Member

    Dec 23, 2010
    200
    6
    Hi all,

    I am looking for a signal generator needed to set up my little laboratory in my home to make my electronics experiments, and looking in the web I realized that the prices are not so cheap, from $300 and so on..

    So I thought to buy a AD9851 DDS Signal Generator and connect the output to a MOSFET Push Pull Amplifier with OPAMP, connected to my regulated 30V - 5A Power Supply.

    Is my idea good enough to start my little project, or maybe, where I can find cheap signal generator?
     
  2. Jotto

    Member

    Apr 1, 2011
    159
    17
    I would get a true function generator. This one is to 2 Mhz.

    http://cgi.ebay.com/EZ-MODEL-FG-700...2824?pt=BI_Signal_Sources&hash=item2eb5b65c08

    The one I use is a bit higher in frequency.

    Cheap one would be a Vellman MK105 Signal Generator Project Kit about 5 bucks, but only good to 1kHz. There are more kits that go higher. Plenty of drawings if you want to make your own also.

    If you want a 2Mhz, you would be much better off getting a unit that was made by a good company, the specs are going to be better along with the circuit design as well as function of the unit.
     
    Last edited: Jun 11, 2011
  3. wayneh

    Expert

    Sep 9, 2010
    12,155
    3,061
    Depending what your needs are, consider a software solution, using an old PC or even an iPhone. There are some handy and free apps for that. Of course if you need frequencies far above audio range, you'll need something else.
     
  4. simo_x

    Thread Starter Member

    Dec 23, 2010
    200
    6
    Hi guys, thank you for your replies.

    I think my idea is not good enough.. My power supply is not dual, so first I should need a negative reference to amplify the negative output. Like a stupid, I did not pay attention to it.

    Would be great to obtain a negative variable reference for -30V. I saw that it's possible starting from a 555 (for his maximum rating, not 30V :D ), but that type of circuit provide just a few mA of source in addition to the approximately 1.5 Voltage drop op the IC, so it is not the best solution.

    Maybe with operational amplifiers.. Or obviously a transformer..
    Any idea?

    Regards,
    Simon
     
    Last edited: Jun 12, 2011
  5. DickCappels

    Moderator

    Aug 21, 2008
    2,664
    634
    You could build a dual supply.

    The AD9851 is an excellent choice and this method is the wave of the present. It does take a lot of overhead in the way of firmware.

    Here is a buffer that should be adequate past 20 MHz:
    http://www.cappels.org/dproj/A_DC_to_20_MHz_amplifier/A_DC_to_20_MHz_amplifier.html

    If you can get your hands on a MAX038 (expensive when you can find them) you can try this (including power supply):
    http://www.cappels.org/dproj/functsweep/functionswp.html

    Anybody up to designing a discreet equivalent to the MAX038?
     
  6. MrChips

    Moderator

    Oct 2, 2009
    12,449
    3,370
    Never overlook the simple solutions. We all have a PC with a sound card. You can generate a lot of different signals with that.

    Also the good ol' 555 timer is a great little signal generator.
     
  7. simo_x

    Thread Starter Member

    Dec 23, 2010
    200
    6
    Hi guys, finally I have already bought that little DDS I linked above which use a AD9851. :rolleyes:
    As I asked for the VRMS output the seller told me that is 5V. I am thinking about amplify the signal with a non inverting amplifier, and off course with a dual voltage power supply I will mount in these days.

    I am just not sure about what operational amplifier use, the frequency output of the DDS is about 50MHz, so when I will know which OPAMP to use, I will determine the voltage supply for the little circuit..

    Can you suggest me one that I could use? Also I would like, off course, less signal noise as possible, as I know I can use a simple capacitor in parallel to the feedback resistor. Will be OK so simple as it seems or some additional component is required?
    Or maybe another type of amplifier is required?

    Thank you for your interest and for your help.
    Regards
    Simo
     
    Last edited: Jun 22, 2011
  8. atferrari

    AAC Fanatic!

    Jan 6, 2004
    2,652
    767
    Last edited: Jun 22, 2011
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